大话Java异常

package demo1;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.FileNotFoundException;

/*
 * 		ArithmeticException -> 算数异常类
		ArrayIndexOutOfBoundsException（间接子类） -> 数组下标异常类
		NullPointerException -> 空指针异常
		ClassCastException -> 类型转换异常
		NumberFormatException（间接子类）-> 数字格式异常
 */

public class TestRuntimeException {
	public static void main(String[] args) {
		
		
		// 观察检测性异常
		// FileInputStream fis = new FileInputStream("c:/a.txt");
	
		// java.lang.ArithmeticException 算数异常
		int a = 10; 
		int b = 0;
		if (b != 0) {
			System.out.println(a/b);
		}

		// java.lang.ArrayIndexOutOfBoundsException 数组下标越界异常

		int[] arr = new int[3];
		int num = 3;
		if (num >= 0 && num < arr.length) {
			System.out.println(arr[num]);
		}
 

		// java.lang.NullPointerException

		String str = null; 
		if (str != null) {
			System.out.println(str.length());
		}

		// java.lang.ClassCastException

		Exception ex = new Exception(); 
		if (ex instanceof IOException) {
			IOException ie = (IOException) ex;
		}

		// java.lang.NumberFormatException

		String s = "12be"; 
		if (s.matches("\\d+")) {
			System.out.println(Integer.parseInt(s));
		}
		System.out.println("运行程序结束");

	}
}

	try {

		a;

		b;  // 可能产生异常的语句

		c;

	} catch (Exception e) {

		e;

	} finally {

		f;

	}

- 当没有产生异常的时候，程序的执行流程是：a b c f 
- 当产生异常时，程序的执行流程是: a b e f 

public class TestExceptionCatch {

	public static void main(String[] args) {

		// 声明引用指向本类的对象，用于读取文件中的内容

		FileInputStream fis = null;

		try {

			// 随时可能产生文件找不到y异常对象， new FileNotFoundException()

			fis = new FileInputStream("d:/a.txt");

		} catch (FileNotFoundException e) {

			// 打印异常的名称、异常原因、异常的位置等信息

			e.printStackTrace();

		}

		try {

			fis.close();

		} catch (IOException e) {

			e.printStackTrace();

		} catch (NullPointerException e) {

			// System.out.println("输出");

			e.printStackTrace();

		}

	}

}

```

- TestFinally.java
```java
package demo3;

public class TestFinally {

	public static void main(String[] args) {

		int a = 10;

		int b = 0;

		try {

			System.out.println(a/b);

		} catch (Exception e) {

			e.printStackTrace();

			return ;

		} finally {

			System.out.println("无论是否发生异常都会执行");

		}

		System.out.println("程序结束");

	}

}

```

	java.lang.ArithmeticException: / by zero

	无论是否发生异常都会执行

	at demo3.TestFinally.main(TestFinally.java:9)

		import java.io.IOException;

		public class A {

			public void show() throws IOException{

				System.out.println("A");

			}

		}

		```

		SubA.java

		```java

		package demo4;

		import java.io.IOException;

		import java.io.FileNotFoundException;

		import javax.print.PrintException;

		public class SubA extends A{

			@Override

			// public void show() throws IOException {

			// public void show() throws FileNotFoundException {

			// public void show() throws PrintException {

			// public void show() throws Exception {

			public void show() {

			}

		}

		```

	>显然不能抛出更大的异常

public class Person {

	private String name;

	private int age;

	public Person() {

		super();

	}

	public Person(String name, int age) throws Exception {

		super();

		setName(name);

		setAge(age);

	}

	public String getName() {

		return name;

	}

	public void setName(String name) {

		this.name = name;

	}

	public int getAge() {

		return age;

	}

	public void setAge(int age) throws Exception {

		if(age > 0 && age < 150) {

			this.age = age;

		} else {

			// System.out.println("年龄不合理");

			// 手动产生一个异常对象并抛出

			// throw new Exception();

			throw new AgeException("年龄不合理!");

		}

		System.out.println("产生异常的效果");

	}

	@Override

	public String toString() {

		return "Person [name=" + name + ", age=" + age + "]";

	}

}

```

- AgeException.java
```java
package demo5;

public class AgeException extends Exception {

	/**

	 * 
	 */
	private static final long serialVersionUID = 1L;

	// 自定义无参的构造方法

	public AgeException() {

	}

	// 自定义使用字符串作为参数的构造方法

	public AgeException(String msg) {

		super(msg);

	}

}

```

- TestPerson.java
```java
package demo5;

public class TestPerson {

	public static void main(String[] args) {

		Person p = null;

		try {

			p = new Person("张三", -12);

		} catch (Exception e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

		System.out.println(p);

	}

}

```

	demo5.AgeException: 年龄不合理!

	null

	at demo5.Person.setAge(Person.java:33)

	at demo5.Person.<init>(Person.java:15)

	at demo5.TestPerson.main(TestPerson.java:8)

public class Student {

	private String name;

	private int id;

	public Student() {

		super();

	}

	public Student(String name, int id) throws IDException {

		super();

		setName(name);

		setId(id);

	}

	public String getName() {

		return name;

	}

	public void setName(String name) {

		this.name = name;

	}

	public int getId() {

		return id;

	}

	public void setId(int id) throws IDException {

		if (id > 0) {

			this.id = id;

		} else {

			// System.out.println("学号不合理");

			throw new IDException("学号不合理");

		}

		System.out.println("结束");

	}

	@Override

	public String toString() {

		return "Student [name=" + name + ", id=" + id + "]";

	}

}

```

- IDException.java
```java
package demo6;

public class IDException extends Exception {

	/**

	 * 
	 */
	private static final long serialVersionUID = 1L;

	public IDException() {

	}

	public IDException(String msg) {

		super(msg);

	}

}

```

- TestStudent.java
```java
package demo6;

public class TestStudent {

	public static void main(String[] args) throws IDException {

		/*Student stu = null;

		try {

			stu = new Student("小王", -5);

		} catch (IDException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}*/ 

		Student stu = new Student("小王", -5);

		System.out.println(stu);

	}

}

```

	Exception in thread "main" demo6.IDException: 学号不合理

	at demo6.Student.setId(Student.java:30)

	at demo6.Student.<init>(Student.java:14)

	at demo6.TestStudent.main(TestStudent.java:14)